1. Field of the Invention
The present invention relates to an external axial rotary piston blower including two pistons each having dual-wing or double-vane configuration and thus identical among each other. These pistons have surfaces or butt faces which mesh and interengage relative to each other during rotation of a pair of pistons on parallel shafts journalled in a housing that includes a casing runway surfacing or inner peripheral surface of the housing formed with two cylinder surfaces intersecting each other at inlet and outlet openings such that cylinder surfaces or butting faces of the piston with large radius engage against the casing runway surfaces and the butting faces or cylindrical surfaces with small radius on the pistons run against each other alternately as to the cylindrical surfaces with large radius.
2. Description of the Prior Art
Such blowers of quarter-roller type of construction are employed or utilized above all as superchargers for vehicle motors or engines. The strong exhaust noise discharging from such blowers as with all such external axial rotary piston blowers is especially disadvantageous with this utilization or employment thereof as a supercharger for vehicle motors. The exhaust noise results from the repulsing of working or operating medium under compression pressure conveyed from one piston in a chamber before the outlet or exhaust into a conveying or output chamber opening after the foregoing and still under external pressure. This noise development increases with increasing speed subject to formation of diverse, dissimilar and most different and in part very high noise frequencies in a manner impermissible and unacceptable for many applications and employment purposes.
For Roots blowers there was proposed to widen or expand the casing runway surface after the outlet or discharge radially in the entire axial width thereof and moreover beginning from the seal limit or boundary between the piston and casing runway surface in that particular position of the piston in which the piston closes the suction chamber. A damping of outlet, discharge or exhaust noise could be attained thereby, since in this manner there is prevented that the return flow of the compressed operating medium into the conveying or output chamber does not occur in a shock-like or impact-like manner but rather delayed in time over a piston rotational angle of approximately 35.degree. (bulletin of the JSME Vol. 24 No. 189, March 1981, pages 547-553). The noise damping attainable therewith however is not sufficient or adequate and this solution is not transferrable upon the initially noted type of construction of an external axial rotary piston blower. During travel or traversal of the beginning of the radial widening or expansion of the casing raceway surfacing there is noted that a wedge-shaped widening space or chamber opens with Roots blowers between a rounding of the piston and the casing runway surfacing with continuously increasing radial widths. With the piston of the quarter-roller blower there would again occur and take place a shock-like back flow of the compressed operating medium at an edge breaking-off around 60.degree. from the approach surface or butting face parallel to the runway surfacing to the subsequent engagement surface of the piston. Most of all however there has been shown that with the proposal made for the Roots blowers that the frequency disturbing the most cannot be reached at all or can be reached only inadequately.